An electromechanical transmission device can be used as an element in a hybrid powertrain system to control torque and speed output to a driveline transmitted from torque-generative devices. The torque-generative devices typically comprise an internal combustion engine and electric machines. One hybrid powertrain architecture includes a two-mode, compound-split, electro-mechanical transmission operative to receive torque input from the torque-generative devices. Management of the torque inputs to achieve an output includes selective actuation of torque-transfer devices, or clutches, contained in the transmission. Actuation of each clutch is effected via selectively applied hydraulic pressure from a hydraulic circuit. Pressurized fluid through the hydraulic circuit is typically supplied from a hydraulic pump that is driven off of an input shaft from the internal combustion engine.
A vehicle using a hybrid powertrain reduces fuel consumption and improves fuel economy by selectively shutting off the internal combustion engine under specific operating conditions, e.g. when the vehicle is stopped at a stoplight, or coasting. Under such conditions, the engine-driven hydraulic pump is inoperative and unable to maintain fluidic pressure in the hydraulic circuit. A currently applied torque-transfer clutch may deactivate due to leak down of hydraulic pressure. Engineers have addressed the issue of leak down of hydraulic pressure during engine shutoff events by mechanizing an electrically-driven auxiliary hydraulic pump operable to supply hydraulic pressure to the torque-transfer clutches.
There is a need for a control system to operate an electrically-driven auxiliary hydraulic pump, to manage electrical energy consumption by the pump and to control hydraulic fluid pressure to the torque transfer clutches for vehicle operation.